Unless otherwise noted, all content was authored by Chip Taylor, edited by Jim Lovett and Sarah Schmidt, and published by Jim Lovett.

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1) Status of the Population

As most of you know, one of my goals is to make sense of the monarch numbers - both at the overwintering sites and during the breeding season. To this end, I’ve been looking at any data that might show how the spring/summer and early fall numbers can be linked to to numbers of overwintering monarchs. Last July, based on nothing more than my experience over the last 14 years and the degree day data that Janis Lentz put together for different latitudes, I predicted that the number of overwintering monarchs for 2005-2006 would be 5-7 hectares. The actual population measured at 5.91 hectares; I got lucky. The basis for this prediction was pretty shaky and could not be justified scientifically. Subsequently, I came up with another factor that offers real promise for quantitative predictions of the size of the overwintering population from one year to the next. Curiously, this estimator yielded a similar result with the total predicted population of 6-7 hectares. The question now is whether the model that I’m working from can accurately predict the monarch population this coming winter, some 7-8 months before the population is measured. “Impossible!” you say. Yes, maybe, and I do have my doubts after seeing the number of sightings (Table 1) reported so far this spring. The model predicts the monarch population will crash and that the overwintering numbers will be half (or even less) of the 5.91 hectares reported last year. In other words, the numbers could be close to the 2.83 hectares recorded in 2000. As I will point out in the rest of this text, there are some similarities and differences between 2000 and 2006. The similarities are consistent with the model but the differences suggest that the population may not crash. This situation is ideal in that one set of data based on physical factors predicts one outcome, while the other based on observed numbers of monarchs predicts another. The development of the population this year should provide a good test for the physical factor model.

The numbers of monarchs reported to Journey North each March and April from 2000 through 2006 are summarized in Table 1.

Table 1. Number of monarchs sightings recorded by Journey North for in March and April 2000-2006 and total number of hectares measured at overwintering sites in late December of the same year.

Year

March
1-24

March
25-31

April
1-30

Totals

Non-TX (%)

Hectares
(Late Dec)

2006

109 (25)

51 (18)

189 (177)

349 (220)

63

-

2005*

31 (1)

42 (8)

90 (60)

163 (69)

42

5.91

2004*

34 (8)

35 (1)

64 (48)

133 (57)

43

2.19

2003

73 (4)

39 (17)

83 (77)

195 (98)

50

11.1

2002*

133 (8)

50 (21)

71 (66)

254 (95)

37

7.5

2001*

60 (4)

18 (1)

99 (73)

177 (78)

44

9.4

2000

61 (24)

27 (21)

109 (109)

197 (154)

78

2.83

*Years with relatively low numbers of butterflies returning from Mexico.

The first thing you will notice is that the number of monarchs reported this spring (N=349) is higher than for any of the previous years (the next highest is 254 in 2002). When we look at numbers like this we have to ask what they reflect and must consider whether they have any predictive value. If they have predictive value, the numbers in the spring should correlate with the numbers of monarchs recorded in Mexico the following December. A quick inspection of the total numbers through April and the overwintering numbers shows that there is no clear correspondence between the spring sightings and the overwintering numbers. For example, there were 150 sightings in 2000 vs 160 for 2003 and the population crashed in 2000 to 2.83 hectares and increased to 11.1 hectares in 2003. As I’ve pointed out before, there are lots of factors that determine the number of reported sightings, such as the weather, the number of citizens motivated to report their sightings, etc. Looking at the relatively high temperatures and low numbers of days with rain through March and April for much of the country, the conditions this spring would seem to have favored observations of the spring migration. Yet, these numbers have to mean something don’t they? In an effort to understand these data, Janis Lentz carefully scanned the Journey North records for those sightings made in Texas and those recorded outside of Texas. The percentage of the total monarchs observed outside of Texas for the first two months is 37-50% for five of the past seven years. However, it was 78% in 2000, a year in which the population crashed, and 63% this year. So what is similar between 2000 and 2006 that might have caused monarchs to move through Texas rather than concentrating their reproductive efforts in that state? Both are drought years, giving rise to the hypothesis that under dry conditions (causing poor milkweed growth), monarchs keep moving until they find more favorable conditions. If this is what has happened in both of these years, it is great testimony to the adaptability of the monarch to adjust to the prevailing conditions. However, we might ask whether laying eggs late in the return migration outside of Texas contributes to the population as much as would laying those same eggs in Texas.

The consensus among monarch scientists seems to be that the majority of monarchs that reach the overwintering sites each fall originate from the upper Midwest in what is known as the corn belt. The model I’m developing suggests that the most important factor that determines these fall numbers is the number of first generation monarchs that reach the summer breeding areas in May and early June. Most of these first generation butterflies originate in Texas from eggs laid from 15 March to 15 April. The first generation monarchs begin moving north in the last week of April and continue to populate the northern breeding areas through perhaps 14 June at the northern reaches of milkweed. So, we have to ask whether eggs laid outside of Texas result in adults that can contribute to the recolonization of the summer breeding areas in meaningful numbers. The answer is probably not. Here’s why: the developmental time from egg to adult for eggs laid north of 35N latitude is too long (see also “Egg Dumping” below). Consider the following: a number of monarchs were seen in eastern Kansas from 15-18 April. On 18 April, Sarah Schmidt collected 28 monarch eggs from milkweed plants we had placed on the south side of our building in an attempt to attract some of the early monarchs. The eggs were brought indoors and on 29 April most were late fourth instar larvae  a typical developmental rate for larvae raised in our facility. I checked the outdoor plants on the 29th to see if Sarah had missed any eggs and I found one larva - a second instar. It will probably take this caterpillar a total of 50 days to reach the adult stage if temperatures are normal for this period. Emergence of the adult would occur around 7 June and this date appears to be too late for a newly emerged monarch to mature and fly further north. The last date in the spring we have observed directional movement of monarchs to the northeast through this area is 5 June.

If my interpretations of the origins of the monarchs reaching the breeding area and developmental rates are correct, it means that the large number of monarchs seen ovipositing north of 35N is NOT a positive sign with respect to the growth of the population. Hopefully, those monarchs developing on milkweeds in Texas will mature rapidly due to higher temperatures and will experience lower rates of predation from fire ants and other predators (drought conditions such as those occurring in Texas most of this spring lowers predation rates), resulting in a large cohort of first generation monarchs that can move northward. Such an outcome would contradict my current model and expectations; however, such an outcome would be fine. Models are only approximations of reality and need to be refined as new data becomes available. In spite of the ominous signs, let’s hope 2006 is a good year for monarchs!

ADDENDUM
The above text was written on 30 April. On 2 May, I had an experience that reminded me of an earlier spring when monarchs moved north in good numbers. I was exercising my dog along a dirt road near my home in the country. He was being a bit headstrong and decided he wanted to track something in the big bluestem and Indian grass along the road rather than to go home for breakfast. So, I decided to check the milkweeds growing along the margin of the road. I didn’t expect to find many, if any, eggs or larvae. Wow! Lots of chewing on the tops of the plants and as I pulled the leaves back I found first and second instar monarch larvae. I found over a dozen larvae on fewer than a dozen plants. The scene reminded me of pictures we had published in one of our Season Summaries some years back. I couldn’t remember the year but checked the old Season Summaries as soon as I got home. I found what I was looking for on page 6 of the volume for the 1999 tagging season. The pictures below were taken in late April or early May of 2000 along the road to the Colyer Cemetery in southern Douglas county SW of Lawrence. Dr. David Gibo and I had seen a modest number of extremely worn and tattered monarchs resting in the large Scotch pines that predominated at this hilltop location about a week earlier. At the time, I regarded the presence of these larvae as a good sign, one signaling a growth in the population, but, as it turned out, the monarchs crashed in 2000 to an overwintering population of 2.83 hectares. Again, this observation reinforces the parallels I made above between the springs of 2006 and 2000. It also reinforces the hypothesis that it is not necessarily advantageous for returning overwintering monarchs to lay large numbers of eggs north of 35N latitude.

Photos by O.R. Taylor. Monarch larvae feeding at the tops on common milkweed plants adjacent to the Colyer Cemetery, Douglas County, Kansas in late April or early May 2000.

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2) Egg Dumping

Monarch females are usually quite selective as to where they place their eggs. Most eggs are placed singly on young leaves and sometimes on flowers. Older, tougher leaves tend to be avoided. It may be that oviposition has been fine-tuned through selection favoring those females that make the best choices for their larvae. Older leaves appear to contain more latex and may contain other compounds or properties that limit the successful development of first instar larvae. It is surprising then to hear accounts of egg dumping by female monarchs returning from Mexico. Egg dumping refers to the tendency of females to lay tens of eggs per plant. It is not uncommon for people who follow monarchs closely to find 40 or more eggs on plants within a few feet of each other. These observers are frequently alarmed since it appears obvious that there aren’t enough leaves to support all these larvae. Egg dumping does not appear to be adaptive. In addition to the prospect of starvation, large numbers of larvae might well attract predators and parasites. Most of the reports of egg dumping occur north of 35N late in the sweep northward by the monarchs returning from Mexico. Given the clear tendency of monarchs that breed in the summer to distribute their eggs singly on plants scattered over a relatively large area, egg dumping is a bit of a puzzle. This is especially puzzling to me because the females I’ve examined that reach Lawrence in April are reproductively spent. Dissections have shown that these females have little or no fat body and usually contain less than 20 eggs with only a few developing eggs in the ovarioles. Evidently I haven’t examined enough of these females, since some apparently arrive at more northerly latitudes with large numbers of eggs to deposit. As to why they dump the eggs rather than scattering them singly, we can only guess. Perhaps the early spring arrivals have difficulty locating milkweeds and therefore lay numerous eggs once a patch has been found. Given that many of these females are already 8 months old by mid or late April, it may also be that, nearing the end of life, they no longer have the capacity to distribute their eggs singly.

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3) Degree Days

The monarch season is off to a hot start. The accumulated monarch degree days for March and April are shown for Austin and Little Rock in Table 2. Note that the accumulated degree days are substantially above the average for the last seven years for both locations. For directions on the calculation of degree days for monarchs, please see the Teaching with Monarchs section of the January 2005 Update. The high number of degree days translates into faster development for most forms of life, including monarch caterpillars. It is for this reason that I expect the first generation butterflies from Texas and other southern areas to be moving north a bit earlier this year.

This has been an early spring for most plants and insects in eastern Kansas with many “first sightings” being 8-10 days earlier than normal. I sighted the first flowering Asclepias viridis (green antelope horn milkweed) in bloom on the 3 May and the first yellow sweet clover flowers on the 4th. Both are 4-5 days earlier than normal.

Table 2. Accumulated monarch degree days from 1 March through 30 April for Austin, Texas and Little Rock, Arkansas. These data were kindly provided by Janis Lentz.

Degree Days

Year

Austin, TX

Little Rock, AR

2006

816.4

578.7

2005

662.5

442.3

2004

716.4

586.8

2003

675.3

499.1

2002

799.4

488.4

2001

628.9

422.8

2000

609.9

423.0

MEAN

707.7

491.6

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4) Monarch Waystation Publicity

Here at Monarch Watch we’ve made many friends over the years. Many go out of their way to support our program and we appreciate their efforts. Somewhere along the way we hope to meet all of these wonderful supporters. While the Monarch Waystation program is off to a good start, we still need many of our friends to help us promote this program and keep the program rolling. Along these lines, earlier in the year I received a note from Elizabeth Hunter, a long time monarch enthusiast who has worked with Lincoln Brower. Elizabeth has tagged many a monarch at Cape May, New Jersey and has promoted monarchs in many ways. Elizabeth declared that she would be glad to devote one of the garden columns she prepares for the Blue Ridge Country Magazine to Monarch Waystations. Elizabeth was true to her word and an excellent article on our Monarch Waystation program can be found at:

As we mentioned last month we now have a limited number of seed kits available in two versions: a standard kit and a California kit. Once our current inventory runs out, additional kits will not be available until next year so if you would like seeds this year please be sure to order early (Monarch Watch Shop item#125522):

Our call to the public to help in the creation of monarch habitats within gardens has led to many inquiries as to how to restore milkweed in more natural landscapes. The techniques for preparing the soil and planting the seeds or establishing seedlings varies from one portion of the country to another. In addition, since restoration projects should only include species that are native to the area, it is necessary to locate compatible sources of seeds. As these inquiries came in, I found that I couldn’t answer many of the questions. I also realized that it is unlikely that I can ever put together a “one size fits all” text that encompasses all of the different scenarios people are likely to encounter. To get some help, I called on one of my colleagues, Dr. Sharon Ashworth, who has a degree in ecology and experience with restoration, and asked her if she could provide a list of resources to which I could refer those who wish to restore milkweeds and other native plants. Sharon kindly provided the list of books and web sites listed below. Several of the web sites are specific for Kansas but similar resources are available for most states. In addition, Sharon offered this general advice: contact the Natural Resources Conservation Service (NRCS) office to obtain lists of native plants that are approved for restoration in your area. Additionally, look for sources of native seeds and plants that are appropriate for your region on the internet and contact the Native Plant Society for your state or an adjacent state for additional guidance. The Kansas Native Plant Society (listed below) has links to a number of seed suppliers in several states that also provide guidance for restoration. You can also contact your local Natural Resources Conservation Service (NRCS) for advice on incorporating native plants into Conservation Reserve Program (CRP) or Wetland Reserve Program (WRP) plantings.

The international connections we make through Monarch Watch continue to amaze me. Last month’s Update contained an article by Cristina Loayza from Leonardo Da Vinci School in Lima, Peru about her use of monarchs to introduce students to science. Shortly after the Update was distributed, we received a note from Alison Holmes, a primary school science teacher at the Dar Al Fikr School in Jeddah, Saudi Arabia. Alison described how the students collected what she took to be monarch caterpillars from the milkweeds growing in the schoolyard and brought them into the classroom to study their metamorphosis and life cycle. Alison’s monarchs are not the monarchs we know; rather, they represent the Old World equivalent to the monarch - the plain tiger, Danaus chrysippus. Like the monarch, the plain tiger is one of the world’s most interesting butterflies. This species is widely distributed in Africa (where it is known as the African monarch), Asia and Australia. Many of the behaviors seen in monarchs are represented in this species, but this butterfly is actually more closely related to the queen, Danaus gillipus, than it is to the monarch. Like the queen, but unlike the monarch, the scent pouches located on the upper-side of the hind-wing of the males are well developed and play a significant role in courtship and mating. This species is also involved with mimicry complexes throughout its range.

There are many informative web sites that describe the biology and distribution of Danaus chrysippus. Listed below are three of the best sites I found in a brief search of the web.

Abstract of a paper describing a bacterium transmitted within the eggs that kills the males but not the females in some populations:

Alison was kind enough to send photos of the plain tiger (African monarch) raised by her students. It is hard to be sure, but the milkweed in the background of one of the photos appears to be Calotropis procera, a West African species that is now widely distributed along coasts on islands in the Caribbean and other sites with sandy soils.

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8) Hawks ans Monarchs

I love to get to get together with monarch biologists to share stories about our favorite organism. The stories go better with beer of course and it was while enjoying a local brew in the company of several monarch biologists at the Entomological Society of America conference at Alisomar in 2004 that Bob Pyle related his observation of seeing a red tailed hawk chase down a monarch. I’m sure I nodded in understanding, hopefully concealing my disbelief - after all Bob has a reputation for veracity. A hawk chasing a monarch! Would you believe it? The red-tails I watch catch rodents. The young red tail pictured below is holding a wood rat it caught just outside my window at Monarch Watch. Anyway, I was willing to cut Bob some slack but now must apologize to Bob for ever doubting him  even silently. Recently, I received a note from Doug Green, a hawk watcher from Cleveland, Tennessee, who observed broad-wing hawks feeding on monarchs while in flight during their migration in September. To quote Doug: “perhaps the broad-wing hawks, flying in ‘kettles’ of hundreds or thousands, have chosen to migrate with the monarchs, for an ‘in-air’ energy source”. This is certainly an interesting observation and it is plausible that both hawks and monarchs would be using the same thermals in which to soar and glide as they migrate. If you know of any hawk watchers, you might get the word to them that any interactions they observe among hawks and monarchs should be noted and reported.

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9) Western Monarchs by Mia Monroe

Monarchs dispersing from the numerous coastal overwintering sites lingered along the coast of California longer than expected, treating observers at sites from Ardenwood to Pacific Grove and as far south as Santa Barbara to monarchs to the very beginning of spring. David Lange from Ellwood reports: "Many of the Ellwood Monarchs left the area in late February but a couple thousand stayed while a cold front, with rain for the coast and snow for the surrounding foothills, came to the south coast. Observers in the local neighborhoods commented on the large numbers of butterflies still hanging around through early and middle March. When warm weather arrived in late March the remaining Monarchs resumed the migration and departed the area."

Friends of Ellwood also request that you keep in touch with them through their new website: www.fotec.org

Monarch scientist and author of Chasing Monarchs, Dr. Robert Michael Pyle, sends this note from the western field:

On March 18, Bob Pyle presented a public talk on the western monarch migration in Salt Lake City, organized by the Utah Lepidopterists and the Utah Museum of Natural History, and hosted by Patagonia. As readers of Pyle's Chasing Monarchs (Houghton Mifflin, 2000), will recall, the state of Utah played a much larger part in his autumn, 1996, journey on the trail of western monarchs than he had guessed it might. Following the talk, seasoned lepidopterist Jacque Wolfe told Pyle that his conclusions confirmed Wolfe's own observations and those of other Utah lepidopterists who had noted monarchs migrating southward rather than westward through their state. (Mia Monroe's observations along Utah's Green River in September, 1996, echoed the same pattern.) For more details, see Brower, L. P., and R. M. Pyle. 2004, “The interchange of migratory monarchs between Mexico and the western United States, and the importance of floral corridors to the Fall and Spring migrations”. In G. Nabhan (ed.), _Conservation of Migratory Pollinators and their Nectar Corridors in North America_. Arizona-Sonora Desert Museum, Natural History of the Sonoran Desert Region, No. 2. University of Arizona Press, Tucson, Arizona.

Visitors to the Santa Cruz area will have a new place to learn about monarchs: the Pacific Migrations Visitor Center/Museum at New Brighton Beach opened April 7.

In San Francisco, check out monarchs on the wing in "The Butterfly Zone: Plants and Pollinators" at the Conservatory of Flowers in Golden Gate Park through October 29.

View a few special butterfly gardens on a free self-guided tour of 60 Alameda and Contra Costa County gardens at the May 7 Bringing Back the Natives Garden Tour. www.BringingBackTheNatives.net

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10) Project MonarchHealth

Project MonarchHealth is a survey of the occurrence of the protozoan parasite Ophryocystis elektroscirrha (OE), which parasitizes monarch butterflies. This parasite is not harmful to humans; however, it can harm the butterflies by inhibiting normal growth and lowering butterfly survival in the wild. To check for parasites, surveyors can swab the abdomen of live butterflies to collect parasite spores. MonarchHealth citizen scientists help scientists map the location and infection levels of OE in monarchs throughout the United States and determine how much disease the parasites cause.

This project is designed and coordinated by Sonia Altizer and Natalie Kolleda of the University of Georgia. For more information on how you or students could contribute to this study, please visit www.MonarchParasites.org or send an email with your inquiry to monarch@uga.edu

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11) Spring Open House & Plant Fundraiser

You are cordially invited to join us on Saturday, May 13th 8am-3pm for our annual Spring Open House and Plant Fundraiser at our facilities on West Campus at the University of Kansas in Lawrence. We are located in Foley Hall (2021 Constant Avenue) near the greenhouse. Nearly 4,000 butterfly plants (both annuals and perennials) including seedlings of seven milkweed species, will be available (modest contributions are suggested). We will provide refreshments, lots of show & tell, videos and games for children, iChat videoconferencing demonstrations, and, of course, monarch butterflies!

We hope to see you there, but if you can't make it to Lawrence we'll have photos and maybe a webcam or two for you to check out online during the day - for more information and a map visit

Monarch Watch is a not-for-profit educational outreach program based at the University of Kansas. We manage several educational, conservation and research programs - focusing on the monarch butterfly, its habitat and the spectacular fall monarch migration.